There is often a need to apply printing to articles having at least one portion which is of non-round cross-sectional shape, for example a bottle, the body of which may include at least a portion of elliptical cross-section which may or may not be symmetrical. Such printing may typically be applied by means of a screen printing process using an apparatus with at least one holding arrangement for holding the respective article to which printing is to be applied, the holding arrangement being disposed pivotably about an axis which is not at the center point of the article. The apparatus used includes a screen printing stencil and a squeegee, which can also be referred to as a doctor, which is displaceable relative to the screen printing stencil.
In a screen printing process which is carried out using the above-indicated apparatus, as disclosed in German laid-open application (DE-OS) No 25 30 360, the holding arrangement is carried by a chain which is flexible in a plane which extends parallel to the direction of movement of the article during the printing operation and normal to the screen printing stencil. Associated with the chain in the region of the screen printing stencil is a guide portion in the form of a cam member whose surface which co-operates with the chain is adapted to the configuration of the surfaces of the article to which printing is to be applied. The holding arrangement which is carried by the chain is reciprocated between two limit positions. In one limit position, the article to which the printing is to be applied is received by the holding arrangement and the article is then passes through the printing station while being carried by the holding arrangement, whereupon in the outer limit position of the reciprocating movement the object with printing thereon is removed from the holding arrangement and then the latter is moved back into the first limit position again, to receive the next following article. That means that the position at which the article with printing applied thereto is removed from the holding arrangement does not coincide with the position at which the fresh article to which printing is then to be applied is introduced into the holding arrangement. On the contrary, between those two positions there is a distance which corresponds to the transportation step which the holding arrangement is required to perform between the position for receiving an object and the position for releasing same.
Screen printing apparatuses which are used for example for printing on hollow articles such as bottles and other containers are generally provided with or combined with a transportation arrangement for the articles. In such an assembly, the articles are moved stepwise from a feed position to which they have been moved for example by a conveyor device disposed upstream of the assembly, into a receiving position in which they are received by the holding arrangement. The holding arrangement moves the article through the processing station, for example a printing station, and then passes into a discharge position in which it releases the article with printing applied thereto, for the article possibly to be carried away from that location by a discharge conveyor assembly.
It is also possible and in every way conventional practice for the screen printing apparatus to include a plurality of processing stations through which the article is passed with a stepwise movement in order to be subjected to successive processing operations. The stations involved may include for example a station for removing dust, a further station for applying a flame treatment to the article, one or more stations for applying printing to the article and stations in which the printing ink on the article is dried.
The length of the transportation stepping movement between the individual stations will normally be established in dependence on the greatest length of the printed image to be applied to the article and thus possibly also the maximum size of the article to which printing is to be applied in the respective apparatus. The result of those considerations is that the transportation step is utilised in its entirety for the printing operation only in those situations in which articles are to be provided with a printed image thereon, the extent of which requires during the printing operation a movement which corresponds to the length of the actual transportation stepping movement. In all cases in which therefore the article is to be provided with printing which is of a shorter extent in the printing direction, the article is transported by a distance which is greater than that which is technically required to perform the printing operation, with the result that the through-put of the apparatus and therefor the level of productivity thereof is lower than would be possible from the printing procedure point of view. That disadvantage is also encountered in other known screen printing apparatuses which are used for applying printing to articles which are of non-round cross-section and in particular substantially elliptical articles. Added to that is the fact that the length of the transportation step when moving the article without simultaneously applying a treatment thereto is also fixed by the transportation step required for the printing operation when printing on the largest possible article capable of being printed upon in the screen printing apparatus, which transportation step is normally greater than that which is required for the actual transportation operation. That is also due to the fact that the stepwise transportation movement of the articles from one station to another with the usual transportation arrangements which perform a reciprocating movement presupposes that the distances between the individual stations, in the region of the transportation arrangement, are equal.